Many telecommunication components used in cellular and landline telephone networks are designed to efficiently transmit human voice signals over voice communication channels. For example, a digital voice coder (vocoder) uses linear predictive coding techniques to represent sampled voice signals in compressed form. These linear predictive coders filter out noise (non-voice signals) while compressing and estimating the frequency components of the voice signals before being transmitted over the voice channel.
It is sometimes desirable to transmit both audio signals and digital data over a wireless telecommunications network. For example, when a cellular telephone user calls “911” for emergency assistance, the user may wish to send digital location data to a call center over the same channel used to verbally explain the emergency conditions to a human operator. However, it can be difficult to transmit digital data signals over the voice channel of a wireless network because such signals are subject to several types of distortion. For example, encoded data signals traveling over the voice channel of a wireless network can be distorted by vocoder effects caused by the voice compression algorithm.
The need remains for improvements in data communications via the voice channel of a digital wireless telecommunications network. Voice channels are preferred for some applications, especially emergency applications, because wireless voice services, as distinguished from data services, are highly reliable, minimize delay, and are widely available in many geographic areas around the world.
Related information can be found in U.S. Pat. No. 6,144,336 incorporated herein by this reference. Additional disclosure can be found in U.S. Pat. No. 6,690,681 also incorporated by reference. And finally, further relevant disclosure appears in U.S. Pat. No. 6,493,338 also incorporated by reference as though fully set forth. The foregoing patents are owned by the assignee of the present application.